Diatoms: Hidden Climate Heroes

Written by Amy Charlton, Volunteer, Booth Museum of Natural History

Diatoms are single-celled microscopic algae found in marine and freshwater environments worldwide. From puddles to oceans, these tiny organisms play a fundamental part in regulating the earth’s climate.

Like plants, diatoms photosynthesise, removing carbon dioxide from the atmosphere and releasing oxygen. They do this on a massive scale, performing an estimated 20% of the earth’s entire photosynthetic carbon dioxide fixation – that’s equivalent to all the rainforests combined!

Discovering Diatoms

Diatoms are tiny – usually less than the width of a human hair – and the invention of the microscope enabled them to be seen for the first time.

In 1703, someone identified only as ‘Mr. C’ wrote to the Royal Society describing a curious organism they had seen under their microscope. This is generally accepted to be one of the first documented diatom discoveries.

Mr. C wrote of:

rectangular oblongs and exact squares, which were joyn’d together… all of the same size… made up of two parallelograms joyn’d longwise… the texture of every one is nearly the same...” (Philosophical Transactions Vol. 23)  https://royalsocietypublishing.org/doi/10.1098/rstl.1702.0065

We now know that Mr. C was probably describing the Tabellaria diatom, whose cuboid cells form zig-zag colonies joined together by mucus pads. Throughout the century, many more diatom species were identified under the microscope.

In the Victorian era, diatom arrangements became fashionable as miniature curiosities. Arranged in patterns on slides, these tiny artworks would be shown under the microscope at social gatherings. Some great examples can be seen here

The Diatomist from Matthew Killip on Vimeo.

Perfect Proxies

Paleoclimatology – the study of past climates – is crucial to understanding what is happening, and what will happen, to our climate as it warms. Temperature records date back around 150 years, but prehistoric climate conditions can be reconstructed using climate proxies. These proxies can be natural archives such as tree rings, corals, ice cores and marine sediments.

Sediment Superstars

Due to their abundance and robust structures, diatoms make great climate proxies. When diatoms die, their tough silica frustules fall to the sea floor. Here, they lock away carbon and form sediment in layers, providing a timeline of changes in ocean conditions.

Diatoms are particularly useful to look at in sediment because of how they react to their surroundings. They are sensitive to change in their environment and the chemistry of their frustules reflects the water in which they were formed. Different species also have different morphological adaptations to allow them to survive in particular conditions. The absence or abundance of a species can therefore indicate and locate a range of conditions such as surface temperature, acidity, salinity and atmospheric carbon dioxide and oxygen levels.

Access to long-term data such as this enables patterns in natural climate cycles to be identified, with which we can compare more recent anthropogenic (human-caused) climate change. This can provide critical evidence that human activity is contributing to our changing climate, and predictions can be made about what might happen to our climate – and us – if we do not intervene.

Brilliant Bioindicators

Diatoms can also provide us with valuable insight into what is happening within our aquatic ecosystems right now. They respond rapidly to changes in their environment, and species will reproduce or decline in particular circumstances. In optimal conditions, some species can grow into enormous colonies, or ‘blooms’, that are so large they can even be seen from space!